1. Field of the Invention
The present invention relates to a polymer electrolyte and a lithium battery employing the same, and more particularly, to a polymer electrolyte having good uniformity of an anode surface and an improved decomposition suppressing effect of an electrolytic solution at an anode surface by forming a lithium carbonate coating on the anode surface, and a lithium battery having good charging/discharging efficiency, an improved swelling suppressing effect and a good low-temperature characteristic by employing the polymer electrolyte.
2. Description of the Related Art
Lithium secondary batteries using liquid electrolytic solutions use an organic solvent having a low boiling point in order to enhance low-temperature performance. However, use of a low-boiling point organic solvent may give rise to swelling of an electrode assembly or case, if such a battery is allowed to stand at high temperature, resulting in deterioration of reliability and safety of a battery under a high temperature condition.
To overcome these problems, a method of using solid polymer electrolytes has been proposed. Using solid polymer electrolytes reduces danger of leakage of an electrolytic solution, thereby improving safety of a battery, unlike in the case of using liquid electrolytes.
However, using solid polymer electrolytic solutions decreases ionic conductivity compared to the case of using liquid electrolytes. Thus, in order to practically use solid polymer electrolytes in lithium secondary batteries, research must focus on solid polymer electrolytes having high ionic conductivity and good electrochemical stability.
Linear polymers or crosslinkable polymers of homopolymers or copolymers basically having ethylene oxide are mostly used as monomers of ionically conductive polymers for forming the solid polymer electrolytes.
However, the polymers formed from such monomers are susceptible to crystallization so that their characteristics at low temperature are poor. Also, since ethylene oxide has strong affinity to an electrolytic solution, the polymers may move with the electrolytic solution by interaction between the electrolytic solution and the polymer chains, deteriorating mobility of lithium ions.